/* Copyright  2009
   @Author
   Richard Changde Yin            e-mail yinchangde@hotmail.com

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; version 2 of the License.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software
   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA */

/**
 * @filename:  item/type_holder.h
 */
#ifndef COLLAPSAR_ITEM_TYPE_HOLDER_H
#define COLLAPSAR_ITEM_TYPE_HOLDER_H

typedef struct st_typelib TYPELIB;
class String;
class my_decimal;
class Session;
class Item;

/*
  Item_type_holder used to store type. name, length of Item for UNIONS &
  derived tables.

  Item_type_holder do not need cleanup() because its time of live limited by
  single SP/PS execution.
*/
class Item_type_holder: public Item
{
protected:
  TYPELIB *enum_set_typelib;

  enum_field_types fld_type;

  /**
    Get full information from Item about enum/set fields to be able to create
    them later.

    @param item    Item for information collection
  */
  void get_full_info(Item *item);

  /* It is used to count decimal precision in join_types */
  int prev_decimal_int_part;
public:
  Item_type_holder(Session *session, Item *item);

  /**
     Return expression type of Item_type_holder.

     @return
     Item_result (type of internal expression result)
  */
  Item_result result_type() const;

  enum_field_types field_type() const { return fld_type; };

  enum Type type() const           { return TYPE_HOLDER; }

  double val_real();

  int64_t val_int();

  my_decimal *val_decimal(my_decimal *val);

  String *val_str(String* val);

  /**
    Find field type which can carry current Item_type_holder type and
    type of given Item.

    @param session     thread handler
    @param item    given item to join its parameters with this item ones

    @retval
      true   error - types are incompatible
    @retval
      false  OK
  */
  bool join_types(Session *session, Item *item);

  /**
    Make temporary table field according collected information about type
    of UNION result.

    @param table  temporary table for which we create fields

    @return
      created field
  */
  Field *make_field_by_type(Table *table);

  /**
    Calculate lenth for merging result for given Item type.

    @param item  Item for length detection

    @return length
  */
  static uint32_t display_length(Item *item);

  /**
     Find real field type of item.

     @return
     type of field which should be created to store item value
  */
  static enum_field_types get_real_type(Item *item);
};


#endif /* COLLAPSAR_ITEM_TYPE_HOLDER_H */
